Cryogenic liquid propellant tanks are used on space launch vehicles. For example, the X-33 single stage to orbit vehicle comprises multi-lobe cryogenic liquid propellant tanks. A description of the X-33 multi-lobe tanks is provided in U.S. application Ser. No. 09/009,355 filed Jan. 20, 1998, which is incorporated herein by reference.
Prior multi-lobe cryogenic liquid propellant tanks typically use woven composite joints as the joining member with the tank barrel and dome skins bonded to it. Manufacture of a composite joint of the length needed for single stage to orbit vehicles requires massive amounts of tooling and large autoclaves to perform the cure process. After cure, inspection of the composite part is difficult and repairs are usually needed in locations where the tooling did not provide the compaction required for a high performance laminate. Typically, the repair is associated with a reduction in strength. Woven composite joints are susceptible to cracks in the interior of the joint after cure, which are exacerbated by multiple cycles from cryogenic to elevated temperatures. Such cracking reduces the strength of the joint and increases the permeability and leakage through the joint.
Bonding barrel skins to composite preforms also presents many problems. First, manufacturing fit-up of the barrel skin to the preform is very difficult to achieve with the tolerances needed to ensure a high strength bond. Second, the time needed to place the skin onto the joint structure often exceeds the usable out-time of the adhesive used for bonding. Third, inspection of the bond line for strength is not possible with current technology. What is typically done is an inspection for voids or unbonds in the area, but no strength assumption can be made. Fourth, inspection during the lifetime of the vehicle is very difficult with limited repair options.
Another method of joining tank lobes is to use a bolted configuration with radius blocks to support the barrel and dome skins. Bolted designs with radius blocks have the problem of using bolts in tension and bending as the means of transferring load across the joint. Over time, the bolts may require inspection and retorquing that would require access to the inside of the tank. This leads to contamination and a required cleaning which is not practical in a quick turnaround environment. It is also difficult to seal the area where the barrel skins meet the dome skins with this method.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.